Not applicable.
[Federal Research Statement Paragraph]Not applicable.
This invention is generally in the field of turbine power generation systems utilizing off-gas fuels. Combustion turbines are often part of a power generation unit. The components of such power generation systems usually comprise the turbine, a compressor, and a generator. These components are mechanically linked, often employing multiple shafts to increase the unit""s efficiency. The generator is generally a separate shaft driven machine. Depending on the size and output of the combustion turbine, a gearbox is sometimes used to couple the generator with the combustion turbine""s shaft output. Combustion turbines are sometimes recuperated.
Microturbines are relatively small, multi-fuel, modular, distributed power generation units having multiple applications, such as disclosed in U.S. Pat. No. 4,754,607. Microturbines are a recently developed technology for use in such applications as, without limitation, auxiliary power units, on-site generators, and automotive power plants. Microturbines are normally of single-shaft design and generally use a single stage, radial type compressor and/or turbine with an internal generator directly coupled to the turbine shaft. Microturbines offer the capability to produce electricity remotely, without the necessity of an expensive infrastructure to deliver power to end users, thus providing electricity to remote locations at a lower cost per kilowatt than is available from a traditional centralized power plant with its necessary infrastructure of transmission lines.
Generally, microturbines and combustion turbines operate in what is known as a Brayton Cycle. The Brayton cycle encompasses four main processes: compression, combustion, expansion, and heat rejection. Air is drawn into the compressor, where it is both heated and compressed. The air then exits the compressor and enters the combustor, where fuel is added to the air and the mixture is ignited, thus creating additional heat. The resultant high-temperature, high-pressure gases exit the combustor and enter the turbine, where the heated, pressurized gases pass through the vanes of the turbine, turning the turbine wheel and rotating the turbine shaft. As the generator is coupled to the same shaft, it converts the rotational energy of the turbine shaft into usable electrical energy. In a single-shaft microturbine, the turbine, the compressor, and the generator share the single shaft, with the components commonly configured with the turbine at one end of the shaft, the compressor in the middle, and the generator at the opposite end of the shaft.
These microturbine power generation systems can be used to recover energy from off-gas sources. High BTU off-gas is frequently generated as a by-product of processing at oil and gas fields, and low to medium BTU off-gas can be generated from a variety of sources, such as landfills, wastewater treatment facilities, and digesters. Often the cost of recovery and transportation offsite of off-gases would not be economical viable, and the off-gases are simply flared or released into the atmosphere, and the potential energy of the off-gas is lost. Microturbine power generation systems, however, can be used to recover the energy from these high-BTU or low- to medium-BTU off-gases.
Using these off-gases as a fuel source for microturbine systems can, however, be problematic. In particular, the off-gases often contain condensable components that form liquids during the compression process. These liquids can foul the fuel valve assembly and combustor, leading to poorer system performance and deterioration of fuel and combustion system hardware. In cold climates, the liquid can actually freeze and cause the fuel lines to become blocked, restricting the flow of fuel and inhibiting the microturbine from receiving adequate fuel to operate.
Off-gases also typically have impurities that can foul and corrode the microturbine. For example, a high-BTU off-gas may contain H2S, which can condense and form sulfuric acid, while a low-BTU off-gas may contain CO or CO2 that can condense as carbonic acid. These acids are corrosive to process equipment in contact with the off-gas, and can increase the maintenance cost and/or shorten the useful operating life of the microturbine power generation system. It would therefore be desirable to provide a system and method for ensuring that no liquids are formed in the fuel gas supply to the combustor of a microturbine or other turbine power generation system. These means desirably would be adaptable to a variety of ambient conditions at the operating site of the turbine power generation system.
A turbine power generation system is provided for use with an off-gas fuel source, which comprises a first compression means for compressing air; a second compression means for compressing off-gas; a combustion means, such as a catalytic combustor, for combusting a mixture of said compressed air and a fuel comprising said off-gas; a turbine means for converting energy released from said combustion into mechanical energy; transduction means for converting the mechanical energy produced by said turbine means into electrical energy; a shaft linking said first compression means, said turbine means, and said transduction means, to allow mechanical energy produced by said turbine means to be utilized by said transduction means and said first compression means; and an off-gas heating means for heating said compressed off-gas supplied to said combustion means to a temperature greater than the gas dew point of the off-gas. The off-gas heating means is useful for ensuring that no liquids are formed in the fuel gas supply to the combustor.
In one aspect, a method is provided for reducing or eliminating condensation of off-gas supplied to a turbine power generation system, which comprisesheating off-gas supplied to a combustion means of a turbine power generation system to a temperature greater than the gas dew point of the off-gas, using heat generated by the turbine power generation turbine power generation system or using heat generated by compression of the off-gas for supply to said combustion means.
In another aspect, a method of generating power from an off-gas fuel source is provided which comprises compressing a quantity of air using a first compression means; compressing a quantity of off-gas using a second compression means; heating said compressed off-gas to a temperature greater than the gas dew point of the off-gas using a heating means; combusting a mixture of said compressed air and said heated compressed off-gas using a combustion means; converting energy released from said combustion into mechanical energy with a turbine means; and converting the mechanical energy produced by said turbine means into electrical energy with a transduction means, said mechanical energy produced by said turbine means also being utilized by said first compression means.